This invention relates to copolymers of .epsilon.-caprolactone and glycolide, and more specifically, to such copolymers with improved properties especially adapted for use as coatings for absorbable multifilament surgical sutures.
Multifilament surgical sutures such as Vicryl.RTM. poly(lactide-co-glycolide) multifilament suture typically require a surface coating to improve the pliability and knotting characteristics of the suture. A polymer coating which has recently been developed and shows significant promise as a suture coating is derived from a polymer solution of .epsilon.-caprolactone in an appropriate organic solvent. The coating solution is typically applied to the surface of the suture using conventional techniques, and then the solvent is removed. Polycaprolactone is a biocompatable polymer with a relatively low melting point, a property which is essential for good coating characteristics. Additionally, sutures coated with polycaprolactone exhibit enhanced pliability and handling characteristics. Unfortunately, polycaprolactone homopolymer is essentially nonabsorbable because it retains some of its mass and mechanical integrity in vivo for periods up to one year, which is too long for numerous surgical applications.
In an effort to improve the bioabsorbability and other properties of a polycaprolactone coating polymer, the polymer composition has been modified by incorporating copolymerizable monomers or lubricating agents therein. For example, U.S. Pat. No. 4,624,256 discloses a suture coating copolymer of at least 90 percent .epsilon.-caprolactone and a biodegradable monomer, and optionally a lubricating agent. Examples of monomers for biodegradable polymers disclosed include glycolic acid and glycolide, as well as other well known monomers typically used to prepare polymer fibers or coatings for multifilament sutures. U.S. Pat. No 4,791,929 discloses a bioabsorbable coating of a copolymer of at least 50 percent .epsilon.-caprolactone and glycolide. Sutures coated with such copolymers are reported to be less stiff than sutures coated with other materials, and the physical properties of the coated suture are also reported to be acceptable.
Unfortunately, the problem of adequate bioabsorbability of homopolymers and copolymers of .epsilon.-caprolactone for suture coating applications still remains. One of the difficulties a skilled polymer chemist has faced in solving this problem is in developing a faster absorbing polymer of .epsilon.-caprolactone without sacrificing the physical properties of multifilament sutures coated with such a polymer. In view of the deficiencies with the known art polycaprolactone coatings, it would be most desirable to accomplish this goal.